Langmuir 1998, 14, 1263-1271
1263
Lubricant Effect on Noncontact-Mode Atomic Force Microscopy Images of Hard-Disk Surfaces Guangwen Bao and Sam Fong Yau Li* Department of Chemistry and Institute of Materials Research and Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore Received July 24, 1997. In Final Form: November 24, 1997 In this paper we present our results of imaging ultrathin liquid films of perfluoropolyether (PFPE) lubricants on a hard-disk surface using the noncontact mode of atomic force microscopy (AFM). The presence of liquid films on the disk surface is reflected by features resulting from capillary interactions occurring when the AFM tip comes into contact with the lube layer. With the continually increasing tip-sample separation, the features of the capillary forces disappeared gradually and finally the images show a similar topography of the disk surfaces. The results demonstrate that the lubricants spread over the whole surface and coated surface grains of the carbon overcoats smoothly. More lubricants pool in the grain boundaries. The thickness is estimated in the range of 20-30 Å.
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that the lubricant films as thin as a few nanometers do not spread evenly on rough surfaces, as osmotic and disjoining pressures tend to accumulate lubricants in the location of negative curvatures (pores) and deplete in regions of positive curvatures (top of peaks/asperities). Moreover, some people have speculated that Z-dol lubricant (PFPE with OH end groups), even on smooth surfaces, can segregate, because of autophobicity, when its thickness is higher than some critical value.7 These conclusions are based on characterization using surface analysis techniques such as X-ray photoelectron spectroscopy, ellipsometry, infrared spectroscopy etc., as well as the prediction of theoretical models based on the equilibrium between capillary force and disjoining force.1,12-16 In this paper, we present our direct observation of the lubricant films on the carbon overcoats of textured hard disks. These images can give us further insights into the distribution and spreading of the lubricants on the hard-disk surfaces on the scale of several nanometers. The atomic force microscope (AFM) has proven to be a powerful tool in imaging
